Biodegradable fibers for sensing

ABSTRACT

Biodegradable waveguides and their uses with devices, such as medical devices, are described. In one embodiment, an optically transmissive fibrous structure comprising biodegradable fiber waveguides may be disposed on a surface of a bandage. The bandage in combination with the optically transmissive fibrous structure may allow for simultaneously monitoring and covering an injured area of a patient. In one embodiment, the fiber waveguides may be provided as multi-channel/multi-core biodegradable fiber waveguides for transmitting light to and from a patient tissue. In some implementations, the bandage may include hydrogel-based biodegradable fiber waveguides that may deliver therapeutics to an injured patient area.

BACKGROUND

The present disclosure relates generally to medical devices and methods,and more particularly to medical devices that use transmitted light,such as sensors.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentembodiments. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In medicine it is often useful to monitor various characteristics ofpatient tissues, such as skin or internal tissues, as part of an earlyresponse and/or continuing treatment. For example, it may be desirableto use various techniques to initially measure and continuously monitorone or more physiological characteristics of a patient as part of thetreatment process. It may also be desirable to monitor a patient's areaof injury for various characteristics, such as characteristicsindicative of infection or wound healing. Such techniques may utilizedata collected by a sensor, lead, or contact that is typically directlyover or in close proximity to the area of injury of the patient. Forexample, characteristics related to the status or operation of apatient's circulatory, muscular, or neurological systems may beinitially measured and continuously monitored using various sensorsplaced on or within the patient and relayed to some external monitorthat can then be assessed. When needed, sensors may be positioneddirectly on the monitoring site using straps or adhesives and removedafterwards.

Oftentimes, this medical examination may require the removal of abandage from a sensitive tissue or area of injury. This removal couldprove to be detrimental to the health and recovery of a patient with anopen wound, where the exposed tissue may be susceptible to infection orblood loss. Additionally, the sensing and assessment of the variouscharacteristics that are monitored may prove to be a difficult task whenconventional monitoring equipment is unavailable. Other times, such asduring surgery, sensitive and vital tissues may need to be monitored andbandaged simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present embodiments may become apparent upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 illustrates a biodegradable fiber sensing system, in accordancewith particular aspects of the present disclosure;

FIG. 2 illustrates a block diagram of a spectrophotometric system, inaccordance with various aspects of the present disclosure;

FIG. 3 illustrates a portable monitoring system with an integratedbandage sensor, in accordance with particular aspects of the presentdisclosure;

FIG. 4 illustrates a bandage with integrated biodegradable waveguides,in accordance with various aspects of the present disclosure;

FIG. 5 illustrates a cutaway view of a bandage with integratedbiodegradable waveguides for transmission of light to a patient tissue,in accordance with various embodiments of the present disclosure;

FIG. 6 illustrates a cutaway view of a bandage with integratedbiodegradable waveguides for the transmission of light to a detectorfrom patient tissue, in accordance with various aspects of the presentdisclosure;

FIG. 7 illustrates a bandage sensor with multiple biodegradablewaveguides, in accordance with various aspects of the presentdisclosure;

FIG. 8 illustrates a cutaway view of an embodiment of a biodegradablewaveguide, in accordance with various aspects of the present disclosure;

FIG. 9 illustrates an end-on view of an embodiment of a biodegradablewaveguide, in accordance with various aspects of the present disclosure;

FIG. 10 illustrates a cutaway view of an embodiment of a biodegradablewaveguide that can transmit emitted and received light from patienttissue, in accordance with various aspects of the present disclosure;

FIG. 11 illustrates a cutaway view of a micromachined hydrogel waveguideserving to transmit light from a light source to a patient tissue; and

FIG. 12 illustrates a cutaway view of a micromachined hydrogel waveguideserving to transmit light from a patient tissue to a detector ormonitor.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present disclosure will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

The present disclosure relates to the use of waveguides in medicaldevices. Such devices may include a sensor, such as for use with apatient monitoring system, having waveguides for transmitting and/orreceiving optical signals (e.g., light). The waveguides may be in avariety of forms and may be formed from different materials consistentwith any number of desired properties. For example, typical waveguidesmay include silica and other glass-based fiber optics. As may beappreciated, such materials may not lend themselves to a single-use orto uses in which they may be left in a patient, such as during and/orafter a surgical procedure. In contrast, as described within the presentdisclosure, waveguide materials may be constructed from one or morebiodegradable materials such that the waveguides may be integrated intodevices and, bandages, wrappings and so forth that are constructed to beleft in a patient or to otherwise degrade without additional attentionor removal. In one embodiment, the biodegradable waveguides may beoptical fibers formed from large fibrous materials, which may have anumber of layers and channels for the transmission of light to and fromvarious substrates (e.g., skin). In other embodiments, the waveguidesmay be formed from a bulk material, such as a hydrogel. In yet anotherembodiment, the waveguides may be formed from a mixture of large fibrousmaterials and hydrogels. The integration of biodegradable waveguidesinto bandages or other structures may provide access to subepidermaltissues that would otherwise be difficult to continuously monitor whilesimultaneously protecting the monitored area, such as with a bandage.Additionally, a structure utilizing biodegradable waveguides may allowthe implantation of sensors into a patient that will degrade away overtime and, thus, do not require additional invasive procedures to remove.

With the foregoing comments in mind, biodegradable waveguides asdiscussed herein may be used in various medical contexts, such as in theplacement, on or within a patient, of bandages connected to or includingdifferent types of medical sensors or leads. As discussed herein, theterm bandage sensor may encompass any combination of a wound covering(e.g. a bandage) and a sensing component that is used to simultaneouslycover and examine a wound or area of injury. As may be appreciated, suchsensors may be associated with monitoring systems suitable for receivingand processing signals derived from the sensor. By way of illustration,FIG. 1 is a perspective view of an embodiment of a pulse oximetry system10. The system 10 includes a bandage sensor 12 that includes a bandage14 with biodegradable waveguides 16 and a pulse oximetry monitor 18. Thebandage sensor 12 may include an emitter 20 for emitting light at one ormore wavelengths toward a patient's tissue 22 via the biodegradablewaveguides 16. In some embodiments, the emitter 24 may be opticallyconnected to the biodegradable waveguides 16 via a fiber optic connector24. In a similar fashion, a detector 26 may also be provided in thebandage sensor 12 for detecting the light passing through, reflected orfluoresced by the tissue of a patient through the biodegradablewaveguides 16. In an embodiment, the detector 26 may be opticallycoupled to the biodegradable waveguides 16 via a fiber optic connector28.

In one embodiment, such as where the bandage sensor is wrapped around afinger or toe, light may be transmitted through the measurement site,e.g., an injured area, by regions (e.g., termini of respectivebiodegradable waveguides 16) of the bandage sensor 12 that are onopposite sides of the site. However, in another embodiment of thebandage sensor 12, the light emitting and detecting regions of thebandage sensor 12 may be arranged so that light is transmitted into anddetected from the same side of the measurement site, i.e., a reflectancemode. In such an embodiment, the light may be reflected by the tissue 22back through a respective biodegradable waveguide 16 and to the detector26. As discussed, the transmitted and received light may also betransmitted through one or more respective fiber optic connectors 24 and28 connecting the emitter 20 and detector 26 with respectivebiodegradable waveguides 16. Further, in one embodiment, the bandagesensor 12 may be electrically and/or optically connected to the monitor18 as shown. For example, the bandage sensor 12 may be optically coupledto the monitor 18 via cable 30.

The monitor 18 may be configured to calculate physiological parametersbased on data received from the bandage sensor 12 relating to lightemission and detection. The monitor 18 may include a display 32configured to display the physiological parameters, other informationabout the system, and/or alarm indications. In the embodiment shown, themonitor 18 also includes a speaker 34 to provide an audible alarm in theevent that the patient's physiological parameters are not within anexpected range, as defined based on patient characteristics.

In the illustrated embodiment, the pulse oximetry system 10 alsoincludes a multi-parameter patient monitor 36. The multi-parameterpatient monitor 36 may be configured to calculate physiologicalparameters and to provide a central display 38 for information from themonitor 18 and from other medical monitoring devices or systems. Forexample, in one embodiment where the monitor 18 is a pulse oximetrymonitor, the multi-parameter patient monitor 36 may be configured todisplay, on the central display 38, a patient's oxygen saturationreading generated by the monitor 18, pulse rate information from themonitor 18, and/or blood pressure from a separate blood pressuremonitor. Additionally, the multi-parameter patient monitor 36 maygenerate a visible or audible alarm via the central display 38 or aspeaker 40, respectively, if the patient's physiological characteristicsare found to be outside of the expected range. The monitor 18 may becommunicatively coupled to the multi-parameter patient monitor 36 via acable 42 or coupled to a sensor input port or a digital communicationsport, respectively. In addition, the monitor 18 and/or themulti-parameter patient monitor 36 may be connected to a network toenable the sharing of information with servers or other workstations.

Turning to FIG. 2, the figure depicts a block diagram of an embodimentof the spectrophotometric system 10 that may be configured to implementthe techniques described herein. By way of example, embodiments of thesystem 10 may be implemented with any suitable sensor and patientmonitor, such as those available from Nellcor Puritan Bennett LLC. Thesystem 10 may include the patient monitor 18 and the sensor bandage 12(as discussed with respect to FIG. 1), which may be configured toobtain, for example, a plethysmographic signal from patient tissue atcertain predetermined wavelengths.

Bandage sensor 12 may include one or more biodegradable optical fibersor fiber bundles, as discussed herein, in optical communication with thepatient monitor 18. Embodiments of the bandage sensor 12 may be free ofelectronics, metals, and/or other materials that may influence or beinfluenced by a magnetic field. Additionally, in certain of theseembodiments, the bandage sensor 12 may be substantially free of silica,glass and/or other non-biodegradable materials. Certain components ofthe bandage sensor 12, namely a light transmitting biodegradablewaveguide portion 50 (i.e., a biodegradable emitter region) and a lightcollecting biodegradable waveguide portion 52 (i.e., a biodegradablecollector region) are illustrated in FIGS. 4-12 below. Other componentsof the system 10 include a fiber optic element 24 through which light istransmitted from the monitor 18 to the light transmitting biodegradablewaveguide portion 50 and a fiber optic element 28 through which light istransmitted from the light collecting biodegradable waveguide portion 52to the monitor 18 are also depicted. When the system 10 is in operation,light traveling through the fiber optic element 24 may be emitted by thelight emitting biodegradable waveguide portion 50, may pass into thepatient tissue 22, may be absorbed and/or scattered by the tissue, andmay be collected by the light collecting biodegradable waveguide portion52 to pass back to the monitor 18 along the fiber optic element 28.

In one embodiment, a time processing unit (TPU) 54 may provide timingcontrol signals to light drive circuitry 56 within the monitor 18. Lightdrive circuitry 56 may contain a set of emitters (e.g., LEDs, laserdiodes, and so forth) which may be capable of emitting light throughfiber optic element 24. Light drive circuitry 56 may control whichwavelength of light is emitted by turning on a suitable LED configuredto emit light near a certain wavelength. Light drive circuitry 56 mayalso control when light is emitted, and if multiple light sources areused, the multiplexed timing for the different light sources. Lightemitted from the light drive circuitry 56 may be transmitted throughfiber element or fiber bundle 24 to the sensor 12 and may be transmittedout of the light emitting biodegradable waveguide portion 50 into thepatient tissue 22. The light may be absorbed and/or scattered by thetissue, and may be collected by the light collecting terminal portion52. The light collecting biodegradable waveguide portion 52 may transmitthe collected light through the fiber optic element or fiber opticbundles 28 to a detector 26 within the monitor 18. It should be notedthat, as shown in FIG. 1, the emitter 20 (and/or light drive 56) anddetector 26 may be contained within a separate housing or structure,such that the emitter 20 and detector 26 may be electrically connectedto the monitor 18 and optically connected to the bandage sensor 12.

The TPU 54 may also control the gating-in of signals from the detector26 through an amplifier 58 and a switching circuit 60. These signals maybe sampled at the proper time, depending upon which of multiple lightsources is illuminated, if multiple light sources are used. In oneembodiment, the received signals from the detector 26 may be passedthrough an amplifier 62, a low pass filter 64, and/or ananalog-to-digital converter 66 for amplifying, filtering, and digitizingthe received signals. The digital data may then be stored in a queuedserial module (QSM) 68, for later downloading to the RAM 70 as the QSM68 fills up. In an embodiment, there may be multiple parallel paths forseparate amplifiers, filters, and A/D converters for multiple lightwavelengths or spectra received. This raw digital diagnostic data may befurther sampled by the circuitry of the monitor 18 into specificdiagnostic data of interest, such as pulse rate, blood oxygensaturation, and so forth.

In various embodiments, based at least in part upon the value of thereceived signals corresponding to the light detected by detector 26, amicroprocessor 72 may calculate a physiological parameter of interestusing various algorithms. These algorithms may utilize coefficients,which may be empirically determined, corresponding to, for example, thewavelengths of light used. In one embodiment, these algorithms may bestored in the ROM 74 and/or the mass storage 76.

As depicted, the monitor 18 may include control inputs 78, such asswitches, dials, buttons, a keyboard, a mouse, or a trackball, by whicha user may interact with the monitor 18. A display 32 of the monitor 18may be used to show the physiological measurements, alarm limits, andother information of interest to a caregiver. Further, mass storage 76may store caregiver preferences, patient information, or variousparameters, discussed above, which may be used in the operation of themonitor 18. Software for performing the configuration of the monitor 18and for carrying out the techniques described herein may also be storedon the mass storage 76 and/or on the ROM 74. The mass storage 76 and/orRAM 70 may also store historical values of various discrete medicaldiagnostic data points. By way of example, the mass storage 76 and/orRAM 70 may store historical or trend values of corresponding to pulserate, blood oxygen saturation, and total hemoglobin, as well as others.

While the preceding describes a conventional embodiment such as may beused in a clinical environment, in other embodiments, the bandage sensor12 may be used in a setting where such conventional monitoring systemsmay be unavailable. For example, it may be desirable to use the bandagesensor 12 for emergency response, at a remote location, or in anon-clinical setting, such as on a battlefield, at an accident site, orin other emergency contexts. FIG. 3 illustrates an embodiment of aportable system 80 for monitoring an injured patient when traditionalhealthcare facilities are not readily accessible. The portable systemmay include a portable device, such as a watch-like device 82 configuredto wrap around a portion of a limb (e.g., a wrist). The device 82 mayinclude a built-in emitter 84 and detector 86 that may couple tobiodegradable waveguides 16 of the bandage sensor 12 via fiber opticconnectors 88 and 90, respectively. As with a conventional monitorsystem, such as the system 10 illustrated in FIG. 1, the portablemonitor system 80 may be configured to calculate physiologicalparameters based on data received from the bandage sensor 12 relating tolight emission and detection. Further, the portable monitor device 82may include a display 92 configured to display physiological parameters,other information about the system, alarm indications and/or otherrelevant data. The device 82 may further include multi-function controls94 such that the device 82 may be configured to monitor any number ofpatient characteristics and display a desired set of data. The device 82may further include a communications port 96 to connect and transmitpatient data to a number of external monitors and/or storage devices.

As noted above, the bandage sensor 12 may include biodegradablewaveguides 16 within a bandage structure 14, which may facilitate themedical examination of an injured area on a patient. The material, shapeand extent of the biodegradable waveguides 16 may vary to suit the typeor function of bandage sensor 12. That is, the biodegradable waveguides16 may be formed from different materials that give rise to a number ofdifferent optical and physical properties. In addition, thebiodegradable waveguides 16 may have dimensions that allow thewaveguides 16 to function as single- or multimode optical guides,allowing a variety of light sources to be used as emitters, such asLEDs, broadband lamps, and lasers. The light sources may couple to thebiodegradable waveguides 16 via a conventional fiber optic cable orconnector, a tapered lens or any similar feature. In one embodiment, thebiodegradable waveguides 16 may be provided as a mesh that covers all ormost of the patient contacting surface of the bandage sensor 12 or maycover select portions of the bandage sensor 12 (such as patterns,patches, strips, edges, and so forth) that provide sufficient area foranalysis, as discussed herein.

FIG. 4 illustrates a bandage structure 14 with biodegradable waveguides16 disposed within a bandage material 100. In an embodiment, the bandagestructure 14 may have two biodegradable waveguides 16, where onerespective biodegradable waveguide 102 serves to transmit light to thepatient tissue 22, and the other respective biodegradable waveguide 104serves to transmit light acquired from the patient tissue 22. It may beappreciated that in some embodiments, the bandage sensor 12 may havededicated areas for light emission and detection. For example, one areaof the bandage structure 14 is predominantly or entirely dedicated tolight emission, (such as due to placement of the biodegradable emissionwaveguide 102) while another area of the bandage structure 14 ispredominantly or entirely dedicated to light reception, (such as due toplacement of the biodegradable reception waveguide 104).

In an embodiment, as illustrated in FIGS. 5 and 6, light may enterbiodegradable emission waveguide 102 through an aperture 106, propagatedown the length of biodegradable waveguide 102 and strike a refractionpoint 108, which may serve to direct the propagating light throughanother aperture 110 towards the patient tissue 22. As shown in FIG. 6,the light that has been directed towards the patient tissue 22 may bescattered, transmitted and/or absorbed by the patient tissue 22. Theresulting scattered, transmitted and/or fluoresced light emanating fromthe patient tissue 22 may then enter biodegradable reception waveguide104 through aperture 112, followed by propagation to refraction point114, whereupon contacting refraction point 114 the light then isdirected down the length of biodegradable waveguide 104 and out throughaperture 116 to a photodetector.

While the preceding describes light transmission and reception usingseparate respective waveguides, in some embodiments these functions maybe performed on the same, i.e., a single, biodegradable waveguide 16.For example, the light may be pulsed (as opposed to continuouslyemitted) to allow the biodegradable waveguide 16 to be substantiallyfree of emitted light at certain intervals. In such an embodiment, thebiodegradable waveguide 16 may allow transmission of light in bothdirections, i.e., toward and away from the patient, with light beingtransmitted toward the patient during light pulses and with light beingtransmitted from the patient between light pulses. By way of example, inone embodiment illustrated in FIG. 7, the biodegradable waveguides 16may be provided as a mesh-like structure 118 on or within the bandagestructure 14. In such embodiments, different portions or strands of themesh-like structure 118 may be associated respectively with lighttransmission and reception. In other embodiments, the entire mesh-likestructure 118 may be used in conjunction with pulsed light transmissionsuch that during light pulses light is transmitted by the mesh-likestructure 118 while between light pulses light is received by themesh-like structure 118.

In some embodiments, the mesh-like structure 118 may allow theobservation of a substantial area of the patient tissue 22 covered bythe bandage 14. For example, in some aspects, it may be desirable forthe waveguides 16 forming the mesh-like structure 118 to deliver lightto the patient tissue 22 such that the light that propagates through thefibers exhibits high loss (e.g., >10 dB/m), i.e., the light may leak orescape through the cladding of the biodegradable waveguide 16. In suchembodiments, the high loss may be a result of the biodegradablematerials, the diameter of the biodegradable waveguide 16, thewavelengths selected, and the like. In some embodiments, the resultinghigh loss may lead to an increased area of observation. That is, lightmay travel through the biodegradable material along the length of thewaveguides 16, and propagate outward from the waveguide along the way,thereby resulting in a broadened area of patient tissue 22 that isexposed to the emitted light and, therefore, monitored. High lossmaterials may further allow the collection of scattered, transmitted,and/or fluoresced light from a broader area of the patient tissue 22,i.e., light collection may occur over a greater area as light may enterthe waveguide 16 along the length of the waveguide 16 as well as throughthe terminal portion of the biodegradable waveguide 16.

In some embodiments, the biodegradable waveguides 16 may be formed usinga drawing process to form biodegradable microfibers. The process may beperformed on specific types of fibers that may, in certain embodiments,allow the formation of complex fiber optic structures, such asmulti-core/multi-channel fibers. In other embodiments, the biodegradablewaveguides 16 may be formed by micromachining a hydrogel, which mayresult in single- or multi-mode optical microfibers. The biodegradablewaveguides 16 may be weaved or positioned such that the biodegradablewaveguides form the mesh-like structure 118. In one embodiment, thebiodegradable waveguides 16 may be provided as an optically transmissivestructure 120 used for light emission and a separate opticallytransmissive structure 122 used for light reception. In order that thelight emitted from optically transmissive structure 120 does notdirectly enter into optically transmissive structure 122 without firstpassing through the tissue 22 of the patient, the optically transmissivestructures may be separated by an opaque barrier 124. Additionally,multiple optically transmissive structures may be employed concurrentlyto sample various areas of the patient tissue 22, such as to ensure thatthe entire area of injury is represented by the collected data. In suchaspects, there may be more than two separate and distinct opticallytransmissive structures (such as 120, 122) disposed within the same orseparate bandages 14 such that there may be multiple sites that lightmay enter the tissue 22 and multiple sites that light may exit thetissue 22. In such embodiments, it may be appreciated that there may bemultiple opaque barriers 124 provided to prevent light shunting, i.e.,direct transmission of light from a light emitting structure to a lightreceiving structure.

Moving now to FIGS. 8 through 10, in some embodiments, the biodegradablewaveguides 16 may be multi-channel optical fibers, such as dual-channeloptical fibers 128. Such fibers may be formed by drawing large diameterfibers and concentric, smaller diameter fibers into microfibers. Forexample, the diameter of the larger, outer fiber may be between about 1mm and about 20 cm before drawing, and tens to hundreds of microns (μm)(e.g., about 10 μm to about 500 μm) afterwards. The smaller fibers (theinner fibers) may have initial diameters similar to that of the outerfiber (inasmuch as the inner fibers are able to be placed within theouter fiber). The drawing process may result in inner fibers withdiameters in the range of 1 μm to 50 μm, resulting in single- ormulti-mode optical fibers. The outer fiber may form an outer channel 130and outer cladding 132 that is spaced from the smaller concentric fibers(that may form an inner channel 134 and an inner cladding 136) by asupport material 138 that fills the outer channel 130. When thebiodegradable waveguides 16 are formed by such a drawing process, thebiodegradable waveguides 16 may exhibit properties resembling single- ormulti-mode optical fibers, depending not only on the dimensions of thechannels, but on which channel is coupled to the light source. That is,light propagating substantially down the multi-mode outer channel 130may have varying pathways. Light propagating substantially down theinner channel 134 may or may not have varying pathways, depending on thesize of the inner channel 134. Thus, it should be appreciated that, withthe foregoing comments in mind, the embodiments described herein may beimplemented using multi-channel/multi-core biodegradable fibers, even ininstances where dual-channel/dual-core fibers are described to simplifyexplanation and description.

In the illustrated embodiment in FIG. 9, a dual-channel biodegradablefiber waveguide 128 formed by the process described above includes anouter cladding 132, an outer channel 130, an inner cladding 136 and aninner channel 134 for transmission of light to and from an area ofpatient tissue 22. The outer and inner claddings may be formed from abiodegradable material, which may be any one or a combination oftextiles. For example, textiles including poly (lactic acids), syntheticand natural silks, cellulose and its derivatives, chitin and chitosanderivatives, alignates, sugars, and poly (hydroxyalkanoates) may degradeaway after a given amount of time after being disposed on or within apatient. In some embodiments, the cladding material may be selected suchthat the material is transparent to wavelengths of interest, which mayallow light to travel down the claddings as an evanescent wave. Forexample, in medical diagnostics, low-energy visible and near-IRwavelengths are often used. Thus, transparencies in the range 0.4μm<λ<1.1 λm may be desirable (e.g., 0.7 μm≦λ≦1.1 μm). For example,materials such as hydroxypropyl cellulose, poly (methylmethacrylate) andcellulose butyrate may be used to construct the outer cladding 132and/or the inner cladding 136. In one embodiment, the outer cladding 132and inner cladding 136 may be formed from cellulose butyrate.

The outer channel 130 may be formed, at least partially, using amaterial that is capable of supporting the inner cladding 136 whileenabling the outer channel 130 to serve as a waveguide. Therefore, incertain embodiments, it may be desirable for the outer channel 130 to beformed from a combination of materials that have refractive indicesclose to air (i.e. refractive indices close to 1). In relatedembodiments, the materials may have a refractive index close to a medium(e.g., water, refractive index of about 1.33) that may fill the cores ofthe biodegradable fiber waveguide 128. In such embodiments, it may bedesirable that the light that propagates down the length of the outerchannel 130 does not experience significant loss (e.g., <10 dB/m) due tothe support material 138 and/or solution. Further, the outer channel 130may be formed from materials similar to those used in the inner cladding136 and outer cladding 132. The outer channel 130 may include particles138 that support the inner cladding 136, for example, polydispersehydroxypropyl cellulose powder (refractive index 1.337).

It may be appreciated that the size, shape, and extent of the particles138 may directly affect the waveguiding properties of the dual-channelfiber 128. Thus, in some embodiments, it may be desirable for thesupport to be relatively stable during the processes used to form thedual channel fiber 128, for example, during the drawing process. In suchembodiments, the particles 138 may have a glass transition temperature(T_(g)) higher than that of the fiber materials. In such embodiments,the drawing process may be performed at a temperature higher than theT_(g) of the fibers, such that the size and shape of the supportparticles 138 is not substantially affected. Conversely, in someembodiments, it may be desirable to deform the size and shape of thesupport material 138, in which case materials may be chosen with T_(g)'ssimilar to or lower than that of the fiber materials.

The inner channel 134 may be formed from the drawing process describedabove.

In some embodiments, an inner fiber with an original (pre-drawing)diameter smaller than that of the original (pre-drawing) diameter of theouter fiber is drawn to a diameter such that the inner channel 134diameter approaches the dimensions of a single-mode optical fiber (e.g.between 1 μm and 50 μm, or between 8 μm and 10 μm). The exemplarydimensions may allow efficient delivery of light by medically usefullaser modalities, such as Nd:YAG, Er:YAG, and CO₂, or LED and broadbandlamp sources, such as tungsten-halogen lamps.

As can be appreciated in view of the aforementioned material andconstructive embodiments, the biodegradable fiber waveguides 128 may beintegrated into the bandage sensor 12 to monitor various patientcharacteristics, as illustrated in FIG. 10. In the illustratedembodiment, a dual-channel biodegradable fiber waveguide 128 is bent toallow light delivery to the patient tissue 22. In other embodiments, thefiber is not bent (i.e., is substantially straight) and delivers thelight to a refraction point 140, similar to those described with respectto FIGS. 5 and 6. In other embodiments, an area where the waveguide 128exhibits a curvature 142 may serve as a refraction point 140 to redirectthe transmitted light. In such an embodiment, light emitted from asource, such as a LED, laser or broadband lamp may enter the innerchannel 134 by way of a focused lens or laser beam, such that the lightpropagates down the inner channel 134 in a single-mode fashion. Uponcontacting curvature 142 of the inner channel 134, the light may bereflected and/or refracted towards the patient tissue 22 which mayscatter, transmit and/or absorb the light.

Upon transmission and/or scattering of the light by the patient tissue22, the light may enter the outer channel 130, which is larger indiameter compared to the inner channel 134 in the depicted embodiment.In some embodiments, the outer channel 130 may have a larger surfacearea available for light transmission relative to the inner channel 134,allowing more light to be collected, i.e., increased light sensitivity.Thus, the light emanating from the patient tissue 22 may enter the outerchannel 130 through aperture 144 and propagate towards a detector. Inthe illustrated embodiment, the light may contact refraction point 146of the outer channel 130 (or the area of curvature 142) and be reflectedand/or refracted such that the light propagates down the outer channel130 and out to a detector. In other embodiments, the biodegradablewaveguide 128 may or may not be bent or curve, and may be coupled to agrating and/or light scattering element, such that light emanating fromthe patient tissue 22 is reflected and/or refracted into aperture 144,propagated down the length of the outer channel 130 and out to adetector.

As previously mentioned, in certain of these embodiments, it may bedesirable to surround one or more biodegradable waveguides with a liquidmedium, for example, a water or a physiological saline solution, to farma gel-like structure disposed on the bandage sensor 12. Thus, in suchembodiments the support material 138 of the outer channel 130 may beselected to closely match the refractive index of such a liquid medium.For example, water and saline both have refractive indices of about1.33. As another example, a 10% glucose solution (refractive index ofabout 1.34) may be used as a source of nutrients to speed recovery of aninjured area, or as an alternative inert liquid medium. Thus, theaforementioned support materials 138, for example hydroxylpropylcellulose (refractive index 1.37), may be chosen to meet a variety ofdesired properties, including having a refractive index similar to asurrounding medium. As may be appreciated in view of these and otheraspects of the embodiments described, as mentioned, the dimensions ofthe support material 138 may also be varied to tailor the properties ofthe biodegradable waveguides 128 for a number of applications. Forexample, in some embodiments the support material 138 may be amonodisperse array of particles of a size consistent with a desiredproperty.

While materials and methods have been described in exemplary embodimentsfor the construction of dual-channel biodegradable fiber waveguides 128with two channels, it should be appreciated that similar methods may beused to construct biodegradable waveguides having more than or less thantwo channels, for example, between 1 and 5 channels. In someembodiments, it may be desirable to construct biodegradable waveguides16 with a single core. To form regular, tube-like structures thatinclude a biodegradable waveguide 16, a number of materials may be usedsuch that above the T_(g) of the material, a tube-like structure (afiber) may be drawn down to dimensions consistent with the particularapplications in which the biodegradable waveguide 16 will be used. Forexample, the materials used may be any one or a combination of textilesand materials including poly(lactic acids), synthetic and natural silks,cellulose and its derivatives, chitin and chitosan derivatives,alignates, sugars, and poly(hydroxyalkanoates). In an embodiment, ahollow glucose tube of outer and inner diameter greater than 1 mm may bedrawn at a temperature around about 146° C. to yield a biodegradablewaveguide 16 that may be a single- or multi-mode optical microfiber.That is, the tubular glucose microfiber may have outer and innerdiameters at or below 500 μm, such as, 500 μm and 50 μm, respectively.

In addition to drawing processes described above, the biodegradablewaveguides 16 may be formed by other methods, such as etching,lithography and machining. With these aspects in mind, in someembodiments, the biodegradable waveguides 16 may be formed by amicromachining process performed on a hydrogel. In such embodiments,illustrated in exemplary FIGS. 11 and 12, a bulk hydrogel 150 isdisposed on the bandage material 100 of the bandage structure 14. Thebulk hydrogel 150 may be formed by maintaining a polymer that is able toabsorb a substantial amount of its weight in water in an aqueoussolution, such as a physiological saline solution. By way of example,the polymer chosen to form the bulk hydrogel 150 may be able to absorbbetween 30% and 80% water by weight.

The bulk hydrogel 150 may also be selected such that the materialexhibits nonlinear optical behavior (NLO behavior). Such NLO behaviormay allow a laser, of properly selected power, wavelength, repetitionrate and focal diameter to machine hydrogel waveguides 152 into the bulkhydrogel 150. Typically, materials that exhibit NLO behavior may havechemical functionalities that undergo a polarization change afterabsorbing a photon. For example, the polymer of the bulk hydrogel 150may be any one or a combination of polymers that are unsaturatedhydrocarbon derivatives, or that have a functionality that absorbs atthe wavelength or wavelengths of interest and undergo a change inpolarization as a result. By way of example, the polymers may besilicone-containing, acrylate derivatives, and/or vinyl arenes (e.g.,poly(2-hydroxyethyl methacrylate) or copoly(2-hydroxyethylmethacrylate-N-1-vinyl-2-pyrrolidinone)). In one embodiment, the NLOproperties of the hydrogel 150 may allow a laser, using correctlyselected parameters, to induce local changes in the refractive index ofthe bulk hydrogel 150 material.

For example, due to the nonlinear absorption of photons by the bulkhydrogel 150 material, a laser with a low repetition rate (e.g. between10 Hz and 1 MHz), focused on a section (e.g., between 1 μm³ and 10 μm³)of hydrogel and with power ranging from microjoules to millijoules mayinduce a change in the material with every irradiative pulse that isperformed in a section confined to the focal volume. Thus, moving thehydrogel 150 with respect to the fixed laser focal point may result information of a three-dimensional single-mode fiber optic structure(diameter in the range of 1 μm to 10 μm) with an asymmetric modificationprofile (areas of different refractive indices). As the focal areadisperses its thermal energy in the time between each irradiative pulse,the change in the hydrogel 150 material may be associated with theabsorption of photons. Conversely, at higher repetition rates (>1 MHz)coupled with lower laser power on the order of nano joules, the thermalenergy resulting from irradiation has a cumulative effect, as thethermal energy may not be able to completely diffuse in the time betweeneach irradiative pulse. Such localized heating may cause a volumeslightly larger than the focal volume, such as a section with diameterof 2 μm to 5 μm, to be affected.

Therefore, the factors responsible for the change in the refractiveindex of the bulk hydrogel 150 material may not be attributed to eachrespective pulse, but rather to an accumulation of laser pulses and thecorresponding cumulated thermal energy. This may result in single-modefiber optic structures with symmetric modification profiles (symmetricaldistribution of refraction indices), as may be desirable with somewaveguide applications. However, it may be appreciated that asymmetricchanges in the refractive index of the bulk hydrogel material may alsohave benefits in certain of these embodiments as described herein. Withthe foregoing comments in mind, in some embodiments, it may be desirableto machine the bulk hydrogel material with high repetition, low powerlaser irradiation to form a hydrogel waveguide 152 with a symmetricrefractive index. In other embodiments, it may be desirable to machinethe bulk hydrogel 150 material with low repetition, high power laserirradiation to form a hydrogel waveguide 152 with an asymmetricrefractive index. In further embodiments, it may be desirable to machinethe bulk hydrogel 150 material using high repetition, low power laserirradiation to form certain sections of a hydrogel waveguide 152 andusing low repetition, high power laser irradiation to form othersections of the hydrogel waveguide 152 such that the resulting hydrogelwaveguide 152 has areas of symmetric and areas of asymmetric refractiveindices.

Returning to FIGS. 11 and 12, the bulk hydrogel 150, having beenmicromachined to form hydrogel waveguides 152, may exhibit a differentrefractive index than the hydrogel waveguide-bulk hydrogel interface154. As a result of this refractive index differential, uponintroduction of emitted light into aperture 156, a substantial amount ofthe light may remain confined within the hydrogel waveguide 152 as thelight propagates towards the patient tissue 22. In one embodiment, asthe propagating light reaches a curvature 158 in the hydrogel waveguide152, the light may contact an optional wavelength-selective element 160,such as a diffraction grating, a prism, and/or a lens. In an embodiment,during manufacture of the hydrogel waveguide 152 the laser power andscan rate may be adjusted such that the micromachining process iscarried out at a low repetition, high power setting, resulting in awaveguide area that is relatively rough in morphology. Such a rough areamay serve as the wavelength-selective element 160 to disperse andrefract only certain wavelengths of light towards the patient tissue 22.The propagating light, having contacted the curvature 158 of thewaveguide (and in some embodiments, the wavelength-selective element160) may then be directed towards the patient tissue 22 through aperture162.

As illustrated in FIG. 12, upon contacting the patient tissue 22, thelight may be scattered, transmitted and/or absorbed and fluoresced to becollected at an aperture 164 of a hydrogel waveguide 166. In certainembodiments, the second hydrogel waveguide 166 may be disposed on anopposite side of the bandage sensor 12 from the hydrogel waveguides 152used for emitting, though in other embodiments the emitting hydrogelwaveguide 152 and the receiving hydrogel waveguide 166 may be providedon the same side of the tissue site. In some embodiments, an opaquebarrier, such as the opaque barrier 124 of FIG. 7, may serve tooptically isolate an emission side from a detection side of the bandagesensor 12 to prevent shunting of light. To allow efficient collection ofthe scattered, transmitted and/or fluoresced light, hydrogel waveguide166 may be machined in such a way as to form a high numerical aperturemulti-mode optical fiber. Such multi-mode hydrogel waveguides may havediameters greater than 10 μm, for example, between 20 μm to 50 μm. Uponcollection into hydrogel waveguide 166, the light emanating from thepatient tissue 22 may, in one embodiment, propagate to awavelength-selective element 168, such that the selected wavelengths oflight may be focused or dispersed down the length of hydrogel waveguide166, through an aperture 170, and out towards a detector. Indeed, insome embodiments, as described with respect to FIGS. 4-6, in which thelight source is pulsed, a single hydrogel waveguide may function as boththe emitting and receiving waveguide.

As may be appreciated with respect to the materials and methods used toconstruct hydrogel waveguides 152, 166, it may be desirable to includefeatures used to deliver therapeutics to the injured patient tissue 22at the sensor site. Therefore, in some embodiments, the bulk hydrogel150 may be doped or treated with any one or a combination ofantibiotics, pain relievers, growth factors, healing agents, antivirals,or any therapeutic compound that does not significantly affect theoptical performance of the hydrogel waveguides 152, 166. In someembodiments, the bulk hydrogel material 150 may itself displayantimicrobial properties. In other embodiments, the therapeutics may bedelivered to the patient tissue 22 directly through the hydrogelwaveguides 152, 166, such that the performance of the hydrogelwaveguides 152, 166 is not significantly affected after elution. Thetherapeutics may elute through the bulk hydrogel 150 or through thehydrogel waveguides 152, 166 over a given period of time (e.g., between2 hours and 2 days), during which the hydrogel waveguides 152, 166, inconcert with the bandage sensor 12, may serve to provide feedbackconcerning the injured area. In other embodiments, it may be desirableto continuously monitor the patient tissue 22 as the therapeutics elutethrough the hydrogel waveguides 152, 166.

In some embodiments, the feedback gained from monitoring the patienttissue 22 via the hydrogel waveguides 152, 166 may be affected by thepresence of such therapeutics. As such, correction factors may beintroduced to account for a known concentration of therapeutics withinthe bandage sensor 12, optically transmissive structure 120 and/or 122,bulk hydrogel 150, and/or hydrogel waveguides 152, 166. The feedback maybe in the form of scattered, transmitted and/or fluoresced light thatmay have distinct signatures characteristic of any one or a combinationof infection, the presence of foreign bodies, the health of the injuredarea and/or indications of when the bandage should be changed.

While the disclosure may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the embodiments provided hereinare not intended to be limited to the particular forms disclosed.Indeed, the disclosed embodiments may be applied to measurements ofblood oxygen saturation as well as other physiological measurements.Rather, the various embodiments may cover all modifications,equivalents, and alternatives falling within the spirit and scope of thedisclosure as defined by the following appended claims.

1. A light conducting structure, comprising: a biodegradable opticallytransmissive structure comprising one or more fibers; and an opaquebacking material disposed opposite a substrate-contacting surface of thebiodegradable optically transmissive structure.
 2. The light conductingstructure of claim 1, wherein the one or more fibers forming thebiodegradable optically transmissive structure do not comprise silica orglass.
 3. The light conducting structure of claim 1, wherein the one ormore fibers forming the biodegradable optically transmissive structurecomprise any one or a combination of poly(lactic acids), synthetic andnatural silks, cellulose and its derivatives, chitin and chitosanderivatives, alignates, sugars, and poly(hydroxyalkanoates).
 4. Thelight conducting structure of claim 1, wherein the one or more fibersforming the biodegradable optically transmissive structure comprise ahydrogel.
 5. The light conducting structure of claim 1, wherein thebiodegradable optically transmissive structure comprises a first and asecond optically transmissive fibrous structure, wherein the firstoptically transmissive fibrous structure transmits light toward thesubstrate-contacting surface and the second optically transmissivestructure transmits light from the substrate-contacting surface.
 6. Thelight conducting structure of claim 1, wherein the one or more fibersare capable of emitting or receiving light along their respectivelengths.
 7. The light conducting structure of claim 1, wherein thebiodegradable optically transmissive structure is provided as a mesh. 8.The light conducting structure of claim 1 further comprising a bandagematerial on which the opaque backing material is disposed on or in. 9.The light conducting structure of claim 1, wherein the one or morefibers are multi-channel/multi-core optical fibers.
 10. Aspectrophotometric system, comprising: a physiological monitor capableof measuring one or more physiological parameters; and a physiologicalsensor capable of communicating with the monitor, the physiologicalcomprising: a light emitting region comprising one or more biodegradablefibers capable of emitting light along their respective lengths; a lightreceiving region comprising one or more biodegradable fibers capable ofreceiving light along their respective lengths; and an opaque barrierpositioned between the light emitting region and the light receivingregion.
 11. The spectrophotometric system of claim 10, wherein thebiodegradable fibers capable of emitting light and the biodegradablefibers capable of receiving light comprise multi-channel/multi-coreoptical microfibers.
 12. The spectrophotometric system of claim 10,wherein the biodegradable fibers capable of emitting light and thebiodegradable fibers capable of receiving light comprise hydrogelwaveguides.
 13. The spectrophotometric system of claim 10, wherein theone or more biodegradable fibers capable of emitting light along theirrespective lengths comprise the one or more biodegradable fibers capableof receiving light along their respective lengths.
 14. Thespectrophotometric system of claim 10, wherein the physiological monitorcomprises a pulse oximetry monitor or a multi-parameter monitor.
 15. Amethod for manufacturing a sensor, comprising: positioning one or morebiodegradable optically transmissive structures within a sensor body;applying an opaque backing layer on one side of the biodegradableoptically transmissive structure.
 16. The method of claim 15, comprisingforming the biodegradable optically transmissive structure byinterweaving or aligning the one or more fibers.
 17. The method of claim15, comprising forming the one or more fibers by micromachining a bulkhydrogel.
 18. The method of claim 17, wherein the bulk hydrogelcomprises any one or a combination of antibiotics, pain relievers,growth factors, healing agents, antivirals, or other therapeuticcompounds.
 19. The method of claim 15, comprising forming the one ormore fibers by drawing one or more biodegradable fibers with diametergreater than about 1 millimeter.
 20. The method of claim 19, wherein theone or more fibers comprise a plurality of concentric forming amulti-channel/multi-core optical fiber.